Wikipedia

Kumquats or cumquats are a group of small fruit-bearing trees in the flowering plant family Rutaceae, either forming the genus Fortunella, or placed within Citrus sensu lato. The edible fruit closely resembles that of the orange (Citrus sinensis), but it is much smaller and ovular, being approximately the size and shape of an olive. The English name “kumquat” derives from the Cantonese pronunciation gam1 gwat1 (given in Jyutping romanization).

They are slow-growing evergreen shrubs or short trees, from 2.5 to 4.5 meters (8 to 15 ft) tall, with dense branches, sometimes bearing small thorns. The leaves are dark glossy green, and the flowers white, similar to other citrus flowers, borne singly or clustered in the leaf-axils. Depending on size, the kumquat tree can produce hundreds or even thousands of fruits each year. The tree can be hydrophytic, with the fruit often found floating on water near shore during the ripe season.

The plant is native to south Asia and the Asia-Pacific region. The popular and best kumquats is from Yangshuo of China, where is a tourist city also. The earliest historical reference to kumquats appears in literature of China in the 12th century. They have long been cultivated in Japan, Taiwan, the Philippines, and southeast Asia. They were introduced to Europe in 1846 by Robert Fortune, collector for the London Horticultural Society, and shortly thereafter into North America.

Uses

Kumquats are often eaten raw. As the rind is sweet and the juicy center is sour, the raw fruit is usually consumed either whole—to savor the contrast—or only the rind is eaten. The fruit is considered ripe when it reaches a yellowish-orange stage and has just shed the last tint of green.
Culinary uses include candying and kumquat preserves, marmalade, and jelly. Kumquats can also be sliced and added to salads. In recent years kumquats have gained popularity as a garnish for cocktail beverages, including the martini as a replacement for the more familiar olive. A kumquat liqueur mixes the fruit with vodka or other clear spirit. Kumquats are also being used by chefs to create a niche for their desserts and are common in European countries.The Cantonese often preserve kumquats in salt or sugar. A batch of the fruit is buried in dry salt inside a glass jar. Over time, all the juice from the fruit is diffused into the salt. The fruit in the jar becomes shrunken, wrinkled, and dark brown in color, and the salt combines with the juice to become a dark brown brine. A few salted kumquats with a few teaspoons of the brine/juice may be mixed

with hot water to make a remedy for sore throats.A jar of such preserved kumquats can last several years and still keep its flavor.
In the Philippines and Taiwan, kumquats are a popular addition to green tea and black tea, either hot or iced.In Vietnam, kumquat bonsai trees (round kumquat plant) are used as a decoration for the Tết (Lunar New Year) holiday. Kumquat fruits are also boiled or dried to make a candied snack called mứt quất.
Variants of the kumquat are grown specially in India.
The kumquat is celebrated annually in Dade City, Florida, U.S.A. with the annual Kumquat Festival.